1. Field of the Invention
This invention relates generally to shiftable variable ratio sprocket chain drives of the kind having an adjustable shifting mechanism operable by a shifting actuator for varying the drive ratio of the drive. The invention relates more particularly to an improved sprocket chain drive of this kind embodying a novel hydraulic shifting system and to a rider propelled vehicle, such as a bicycle, embodying the improved chain drive. The invention relates also to a novel hydraulic connector for such chain drives.
2. Discussion of the Prior Art
Shiftable variable ratio sprocket chain drives of the kind to which this invention relates are most commonly used on bicycles, such as racing bicycles and so-called mountain bikes. The present invention is intended primarily for use on such bicycles and will be described in this context. It will become readily evident as the description proceeds, however, that the invention may be used on other rider propelled vehicles and other devices having a shiftable variable ratio sprocket chain drive of the character described.
A conventional variable speed bicycle of the kind referred to above has a frame, a rear drive wheel and a front steerable wheel, a seat for the rider, a handle bar for steering the front wheel, a rotary crank mounting pedals to be engaged by the rider's feet for rotating the crank with pedaling action, and a shiftable variable ratio sprocket chain drive connecting the crank and the rear wheel. Rotation of the crank in one direction drives the rear wheel in a direction to propel the bicycle forwardly. The crank may or may not freewheel relative to the rear wheel in the opposite direction of crank rotation.
There are at present two different basic types of such sprocket chain drives. While these two types of drives differ in their construction and operation, they share the common features of a shifting actuator mounted on the bicycle in a position conveniently accessible to the bicycle rider and commonly on the handle bar, and a mechanical cable connecting the actuator to the shifting mechanism of the transmission in such manner that adjustment of the actuator by the rider operates the shifting mechanism to vary the drive ratio of the transmission.
The most common type of shiftable, variable ratio sprocket chain drive for bicycles embodies a so-called derailleur shifting mechanism which is operable to adjust the drive ratio of the sprocket chain drive. In this disclosure, "drive ratio" is defined as the number of revolutions of the pedal crank per revolution of the rear wheel. This type of bicycle sprocket chain drive includes front sprocket means associated with the bicycle pedal crank, rear sprocket means associated with the rear bicycle wheel, and a sprocket chain trained about and in driving engagement with the front and rear sprocket means. The front sprocket means is drivably coupled to the pedal crank for rotation of the front sprocket means by the crank. The rear sprocket means is drivably coupled to the rear bicycle wheel for rotation of the rear wheel in a forward direction (i.e. in a direction to propel the bicycle forwardly) by rotation of the rear sprocket means in a forward direction. The rear sprocket means may freewheel in the opposite direction relative to the rear wheel.
At least one sprocket means of the sprocket chain drive comprises a cluster of coaxial chain sprockets of progressively differing diameters. The several sprockets of each cluster are drivably joined for rotation in unison. Associated with each sprocket cluster is a derailleur shifting mechanism including a shifting member which is adjustable axially of the cluster to shift the adjacent portion of the sprocket chain from one cluster sprocket to the next in one axial direction of the cluster to increase the drive ratio and in the opposite axial direction of the cluster to decrease the drive ratio. The shifting member is urged on one of these directions by a derailleur spring.
The derailleur mechanism includes an idler tension sprocket or pulley about which the chain passes and which is spring biassed in a direction to take up excess slack created in the sprocket chain during shifting of the chain from a larger sprocket to a smaller sprocket. This tension sprocket yields in the opposite direction to provide chain slack during shifting of the chain from a smaller sprocket to a larger sprocket and acts to continuously maintain a proper chain tension in all positions of the derailleur shifting mechanism.
A conventional bicycle with either or both front and rear derailleur shifting mechanisms has a separate shifting actuator for operating each derailleur mechanism. Each shifting actuator is connected by a wire cable to the adjustable shifting member of the respective shifting mechanism and includes actuator means (either a single actuator member or a pair of actuator members) operable by the bicycle rider. Each actuation of a shifting actuator involves adjustment or movement of its actuating means which operates the corresponding derailleur mechanism through the corresponding wire cable to shift the adjacent portion of the sprocket chain from one sprocket to the next sprocket of the respective sprocket cluster to increase or decrease, as the case may be, the drive ratio of the sprocket chain drive. A single derailleur shifting mechanism provides a certain range of drive ratios. The two derailleur mechanisms of a bicycle having both front and rear derailleur mechanisms are selectively adjustable individually and in combination to provide a much wider range of drive ratios. Examples of bicycles having such derailleur shifting mechanisms are described in U.S. Pat. No. 4,938,324, dated Jul. 3, 1990 to Van Dyke and U.S. Pat. No. 5,102,372, dated Apr. 7, 1992 to Patterson et al. U.S. Pat. No. 3,899,057 to Carre describes a hydraulic brake system for a bicycle.
Another type of shiftable variable ratio sprocket chain drive for bicycles utilizes a rear wheel shifting mechanism commonly referred to as an internal gear shifting mechanism. This type of sprocket chain drive comprises a single sprocket rigid on the bicycle pedal crank, a single sprocket coupled to the rear bicycle wheel through the gear shifting mechanism, and a sprocket chain trained about these sprockets. The gear shifting mechanism comprises a shiftable gear train which is contained within the central hub of the rear wheel and drivably couples the rear sprocket to the rear wheel. This gear train includes an adjustable shifting member operatively connected to a shifter chain which extends externally of the hub through an axial bore in the rear wheel axle. This shifting member is adjustable in one direction to increase and in the opposite direction to decrease the gear ratio or drive ratio of the mechanism (i.e. the number of rear wheel revolutions per pedal crank revolution). Pulling the outer end of the shifter chain moves the shifting member in one of these directions against the force of a spring embodied in the shifting mechanism.
A bicycle equipped with such a gear shifting mechanism has a shifting actuator which may be similar to that used with a derailleur shifting mechanism. This shifting actuator is mounted on the bicycle in a position easily accessible to the bicycle rider, such as on the bicycle handlebar, and is operatively connected by a wire cable to the shifter chain of the internal gear shifting mechanism. This shifting actuator is operable by the rider to pull on or release the shifter chain in increments in such manner as to step the shifting mechanism through its range of drive ratios.
The existing shiftable variable ratio bicycle sprocket chain drives of the kind discussed above have certain deficiencies which are cured by this invention. These deficiencies result from the fact that each rider-operated shifting actuator of the sprocket chain drives is connected to the adjustable shifting member of the respective shifting mechanism by a wire cable connector comprising a wire cable which extends slidably through cable guides and protective tubes or sheaths secured to the bicycle frame. Operation of the shifting actuator in one direction pulls the cable endwise in stepwise increments against the opposing force of the spring embodied in the shifting mechanism to move the adjustable shifting member of the shifting mechanism stepwise in one direction through its different drive ratio positions. Operation of the shift actuator in the opposite direction releases the cable in increments for stepwise return of the shifting member in the opposite direction through its different drive ratio positions by spring action.
These existing wire cable-actuated shifting systems for variable ratio sprocket chain drives have certain undesirable characteristics which adversely affect the shifting action of the chain drives. Among the foremost of these undesirable characteristics are the following. Dirt and grit tend to accumulate in and thereby resist free endwise sliding movement of the shift cable through the cable guides and sheaths. This resistance interferes with proper shifting action of the chain drives. Further, the wire cables of the cable connectors are quite long and tend to stretch over a period of time. This cable stretch introduces a certain sponginess into the shifting action which greatly interferes with or prevents proper shifting from one drive ratio to another. Moreover, wire cable shifting systems require frequent adjustment to compensate for such cable stretching. Even disregarding the adverse consequence of such cable stretching, the relatively long lengths of the wire cable connectors, particularly the rear wheel connector, introduces a certain play or lost motion into the shifting action which interferes with proper shifting of the chain drives from one drive ratio to another. Accordingly, there is a definite need for an improved shiftable, variable ratio sprocket chain drive of the character described.